p38 battery drain

Can anybody offer any advice. When the car is parked up the battery drains itself if left overnight i have noticed that the park light on the gear selector stays on, Is this normal or is this the fault.

Best bet is to do a search - its more than likely the little box that picks up the signal from your keyfob - the older ones had a habit of waking up the BECM everytime it picked up a wireless network or wireless door bell, then that would kill the battery

New one is about £150 from a Stealers... in the short term, you can disconnect the aerial from the box - it sits under the plastic shelf in boot on the drivers side

I have just had a look and there are two boxes there is a blue one with about four connections and a black one with two connectors do you no wich one it is ??

I believe its the one with the two cables - one of them is an coax aerial cable - thats the one to remove...

You'll still be able to get into the vehicle, you'll just have to be closer...

As I say, do a search - its a very common issue

It’s the black one with 2 connections. The one with the coax is the FM amplifier.
There are 2 plugs, 1 white with 3 wires and a single plug with a blue wire.
It is quite difficult to pull the plastic plug out as it has a tang underneath. It is easier to undo the screw that’s holding it down and lift it out. You can then remove the plug.

It doesn’t do any damage all you are doing is limiting the range of the receiver to stop it picking up stray signals.
I have done a video. I am no actor but you can do a before and after test.
If you google : becm sleep test you will see the video.

Just watched your video,a couple of questions;
Why do you shut the bonnet ?
Why totally disconnect the battery when you can carefully attach the fluke leads without loosing contact at all - and not setting the alarm off if the BBUS has any life in it ?
Why suggest ripping out the BECM for testing when it rarely is the BECM at fault,and a current drain need not be from the BECM being awake ?

A small toggle switch can be put in the signal line from the RF ECU to the BECM which will switch any signals off if in a "Dodgy" area-the doors will have to be locked/unlocked by using the key in the door though. When normal setting is required, just turn the switch on.You can of course buy the updated ECU at around £150.

Just a quick question as I have just had exactly the same problem on mine!.....Are you able to input the code into the radio?......or has your horn stopped functioning?
The fault was traced on mine to corroded terminals behind the airbag on the steering wheel. I had allegedly had a leaking windscreen and the water was dripping onto the steering wheel.
This fault took 3 people nearly 2 weeks to trace!

eightinavee said:

Just watched your video,a couple of questions;
Why do you shut the bonnet ?
Why totally disconnect the battery when you can carefully attach the fluke leads without loosing contact at all - and not setting the alarm off if the BBUS has any life in it ?
Why suggest ripping out the BECM for testing when it rarely is the BECM at fault,and a current drain need not be from the BECM being awake ?

Click to expand...

I shut the bonnet to switch the bonnet open switch. Otherwise the alarm may go off and the instrument cluster reports the bonnet open.
You could probably attach the leads to the battery terminal but I prefer a clean disconnect. When you lift it off whilst trying to maintain a connection you run the risk of making and breaking the connection a couple of times and the becm can just go to EKA lockout.

If the vehicle is unlocked the alarm will never go off.

With a clean disconnect I get a good connection first time every time and it’s less fiddly for anyone whose new to electrics and wants to give it ago. It also tells you that your door electrics are ok after the battery drain.

P38’s can have a problem with the door loom, notably the key switch and the black wire.
You would never know the fault was there until you had an eka lockout and you needed to enter the code and re sync the key. So it is a good opotrunity to test it now.
A faulty key switch can keep waking up the becm and common symptoms are indicators are all on and puddle lamps may come on or flash.

Out of every 10 becm’s I test I have between 4-6 that will not sleep on the bench test due to damage. The constant battery drain corrupts the information in the becm and at worst damages it.
As the becm starts to corrupt it can put voltage on the serial data bus to the door outstations and it buns the front locks out. I get at least one like this every day. All from a flat battery.
It often changes the EMS code, EKA code and even changes the Fob code. It’s like winding down the voltage on your desktop computer. Eventually it corrupts and crashes.

When P38 owners telephone me, I run through everything to do with the receiver and make sure everything has been done their end to try and rectify the drain. If all else fails, it’s an easy comprehensive test.

I find this quite amusing really,LP RR's will happily go to sleep with the bonnet and windows open.Your video says nothing about setting the alarm off by just pulling the battery lead off.(Plus the hassle of resetting the windows/sunroof - esp as the CC outstation switches are dying from old age/coca cola etc.)Then gives current readings in OHMS ?
The testing of the BECM is the LAST thing to do when faultfinding a battery drain issue.The main point being how do you know if the 1/2 odd amp,(Or more.) is being drawn by the BECM staying awake ? Where you get your 4/6 out of 10 failure rate is beyond me.Stray RF signals,aftermarket audio,LPG systems,GSM kit or Sat Nav fitments are all much more common causes of flat batteries.Not even mentioning short cold weather trips,cheap alternators or duff batteries.
All smacks of a bit of free advertising to me.

Where you get your 4/6 out of 10 failure rate is beyond me : Mostly by Royal mail

aftermarket audio,LPG systems,GSM kit or Sat Nav fitments: exactly what it says in the video.
As I said the Alarm doesn’t go off with the vehicle unlocked.

Not even mentioning short cold weather trips,cheap alternators or duff batteries.
All smacks of a bit of free advertising to me: you are confusing lack of battery power with current draw.

I have done it as a simple to follow video and closing the doors and bonnet rules out all the questions I get about whether you need to close them, open them, unlock them, lock them.

It’s just a simple video to follow that offers a simple service if all else fails. When people try the test in the video they often get in touch and I offer free advice and offer wiring diagrams to help.

On the upside you have something to amuse you.

Mmm,confused....... Dont think so,been editing videos have we ? Battery drain and duff batteries/alts all result in the same situation - a non start.BTW the factory sleep current, ( From the BECM SIDS.) is 20-30 mA,not as your vid now shows."The alarm doesnt go off if you disconnect the battery with the car unlocked" Really ? If its an LP with BBUS fitted you only have 17secs to disconnect the battery after switching the key off.

The video has always shown 30-50 but for some crazy reason I wrote the words ohms not milliamps.

Every P38 Range rover I have tested to date has measured between 30 to 50 milliamps when it is asleep.
You are right that Battery drain and duff batteries/alts all result in the same situation but you have to have a logical set of diagnostic steps and checking for current drain is one of them.

It is the logical place to start. If the vehicle goes asleep then you start looking at drop testing the battery ect. It doesn’t even matter which way around you do the tests.

If the video bothers you that much get your camera out and put a better one online. It’s free to do and you can enlighten everyone with your knowledge of P38’s

No,it does not bother me that much,I just think its important for info to be accurate.I've made my point and I wish you luck - there are plenty of them that need repair,most of them belonging to people who cant be bothered to read,look or learn.

try front heated screen fuses, mine suffer it

allemar said:

Can anybody offer any advice. When the car is parked up the battery drains itself if left overnight i have noticed that the park light on the gear selector stays on, Is this normal or is this the fault.

Click to expand...

I have had a similar problem since January and I think I have solved it! I have disconnected the antenna from the Rf module above the rear o/s parcel shelf. The fob now only works when I stand near the door. This is better than a flat battery!!
Electricity providers have been offering 'usage monitors' which send a signal up to 30 metres on frequency 433mhz. (I fitted one recently) This I believe is the frequency used by the RR fob.Every time there is a change in electricity in any near by house (just the fridge kicking in!) a pulse is sent to the monitor in the house, and probably also to the RR locking system. The rr has an interupted sleep and consequent battery drain.)